As described in JP-A-61-105616, for example, a conventional CNC apparatus for controlling a plurality of machines is arranged such that machine tools are connected on a one-to-one correspondence with CNC units, and that each CNC unit is connected to a host unit. Therefore, data is exchanged between the CNC units and the host unit (a cell controller and a program file unit) by serial transfer or via a LAN or the like. The CNC units and the host unit are each equipped with an operator input/output function.
The CNC apparatus in general incorporates a microcomputer, and therefore, software of several hundred kilobytes is used to operate the microcomputer. This software comprises a part program including machining data used in machining a workpiece with a machine tool, and a system program for controlling the motions of the machine tool by interpreting the part program in execution. The software is normally stored in ROM contained in each CNC unit, and cannot be modified easily.
For this reason, with a conventional CNC unit used for controlling a plurality of machine tools, when the system program and the part program need to be changed, the ROM has to be replaced. Another problem of the conventional CNC unit is that the CPU of the host unit and the respective CNC units are loosely coupled, and when changing the system program and the part program, it is necessary to exchange signals and transfer the programs between the CPU of the host unit and a CNC unit, and the host unit and the CNC unit must operate in a pair at all times. Therefore, the transfer speed of data including the system program and part program between the host unit and each CNC unit is relatively slow. When any one of the machine tools becomes unable to operate due to a fault in the system program or the part program, maintenance of the program for recovery to normal operation is complicated.
Therefore, the present invention has as its object to provide a general-purpose CNC apparatus for controlling a plurality of machines, which allows the system program and the part program to be changed easily and quickly, and which ensures the ease with which the system program or the part program can be maintained even when the program becomes not executable, and which can handle various kinds of machining operations.